The present invention relates to a device for driving shutter of a camera in which a bimorph element (a piezoelectric element) displaceable or deformable by the application of a voltage thereto is used as an actuator.
A conventional circuit of a device for driving a shutter of a camera in which a displacing or deforming effect of a bimorph element caused by the application of a voltage thereto is used as a force for driving a shutter of a camera is shown in FIG. 8 of the appended drawings. In FIG. 8, V.sub.H is a high voltage electric source line to which connected is a capacitor for an electronic flash of a camera. BI is a bimorph element. Q1 is a transistor which is turned on at the time of opening the shutter to charge the bimorph element BI. Q2 is a transistor which is turned on at the moment of closing the shutter to discharge the electricity of the bimorph element B1. DO is a diode for preventing a potential of the connecting point P of the bimorph element BI and the transistor Q1 from becoming a highly negative voltage at the moment of turning on the transistor Q2. RO is a resistance connected in parallel to the bimorph element BI and this resistance RO is provided for the purpose of preventing a leak current from being fed to a condenser capacitance of the bimorph element BI to erroneously operate the device for driving a shutter at other time than the time of opening the shutter.
By operating the transistors Q1, Q2 in such conditions as shown in the following table 1, the bimorph element BI is charged or discharged to be displaced or deformed so that the shutter can be opened or closed.
TABLE 1 ______________________________________ usual time opening the shutter closing the shutter ______________________________________ Q1 OFF ON ON Q2 OFF OFF ON ______________________________________
As shown in FIG. 8, a method of charging the bimorph element with a constant current is known. However, in this case in which the abovementioned resistance RO is connected in parallel with the element BI, a small value of this resistance RO is not preferable for obtaining a constant current and on the contrary a large value of the resistance lowers the effect of preventing a leak current.
As a result, when a resistance is connected in parallel to the bimorph element, it is difficult to set the value of the resistance, and a problem of preventing erroneous operation of the device for driving a shutter has not been sufficiently solved yet.
For the purpose of solving the abovementioned problem, the present invention is made. And an object of the present invention is to prevent erroneous operation of a divice for driving a shutter in which a bimorph element is uses as an actuator caused by a leak current or the like, by short-circuiting the bimorph element all the time except an exposure time.